The present invention relates to a blood pumping system capable of generating a backflow warning to warn of blood backflow through a non-occlusive blood pump and selectively disabling the backflow warning when electrical interference would cause a false backflow warning to be generated.
Blood pumping systems are used in clinical situations, such as open-heart surgery, to provide blood circulation for the patient undergoing the surgery. A typical blood pumping system draws blood from a patient's venous system into a conduit connected to the inlet of a blood pump and pumps it back into the patient's arterial system via a conduit connected to the outlet of the blood pump. The conduit may be connected to other devices to provide blood filtering, heating, oxygenation, collection, etc.
While various types of blood pumps have been used in blood pumping systems, one particular type of pump that has been found to be generally advantageous is a centrifugal pump. Such a pump is described in U.S. Pat. No. 4,589,822 to Clausen, et al. One characteristic of centrifugal blood pumps is that they are "non-occlusive," which means that when connected to a conduit, the mechanical structure of the pump allows blood to flow in the direction opposite the blood pumping direction. As a result, even though a non-occlusive blood pump may be turned on and operating, blood may actually flow backwards through the pump in the wrong direction, which may have adverse consequences for the patient.
As is known, the primary adverse effect of such backflow is that air may be drawn into the blood within the pumping system and pumped into the patient when the blood flow is later reversed to the proper direction. If the perfusionist or doctor detects that air has been drawn into the pumping system, there are procedures to prevent the air from being pumped into the patient. However, these procedures are tedious and/or time-consuming. Moreover, the perfusionist or doctor may not notice that air has been drawn into the system.
Backflow occurs when the output pressure of the blood pump is exceeded by the load pressure of the patient. This load pressure depends on such factors as the resistance of the arterial and venous systems of the patient, which may vary with the physical size and age of the patient; the resistance of the external pumping system; the relative height of the patient with respect to the blood pumping system; etc. If for any reason the load pressure should happen to exceed the output pressure of the pump, backflow will occur.
Blood pumping systems have previously been designed to generate a backflow alarm to warn the perfusionist or doctor of blood backflow. An example of such a system is disclosed in U.S. Pat. No. 4,778,445 to Hubbard, et al.
Although it is desirable to generate a blood backflow alarm, false alarms may be generated due to electrical interference. One example of such interference is "Bovie" interference, which is caused by the use of an electrocauterizer unit during surgery. In such a unit, high-energy radio-frequency ("RF") radiation is used to heat the metal tip of the unit. The RF radiation can interfere with various electronic equipment typically used during surgery, including an electronic blood pumping system as described above.
Although the amount of electrical interference caused by an electrocauterizer unit can be reduced somewhat by using conventional electro-shielding techniques, that approach is generally inadequate. That is particularly true in the case of a blood pumping system utilizing a Doppler-type flowmeter, which is very sensitive to electrical interference due to the fact that such a flowmeter uses a transducer at the end of a relatively long cable, which tends to act as an antenna and the fact that the electrical signals the flowmeter utilizes to determine flow are typically of relatively small magnitude. Thus, when high energy electrical interference is encountered, it is difficult if not impossible to separate the small signals indicative of flow from the much larger signals caused by the electrical interference.
The generation of false alarms during surgery is problematic due to the unnecessary stress and annoyance induced in the operating room personnel and may also cause such personnel to lose confidence in the accuracy of the medical equipment that generates such an alarm.